1. Field of the Invention
This invention relates to an improved process for the preparation of S-substituted phosphorodichlorothioates, which are useful as intermediates for the manufacture of insecticides.
2. Description of the Related Art
The compounds produced by this process are useful as intermediates in the preparation of O,S-disubstituted phosphorochloridothioates, which are, in turn, useful in the preparation of organophosphorus pesticides described in, for example, U.S. Pat. Nos. 3,374,293, 3,784,654 and 3,839,509. The phosphorodichlorothioates of the present invention can be converted to O,S-disubstituted phosphorochlorothioates by reacting them with an alcohol in the presence of an acid scavenger (i.e., a tertiary amine).
There are many known processes for preparing phosphorodichlorothioates, and the following references are illustrative of these processes: Synthesis of alkyl dichlorodithiophosphates, Izv. Akad. Nauk SSSR, Ser. Khim., (11), 2620-22; Synthesis and fungicidal activity of O,O-diaryl S-isopropyl phosphorothioates, Proc. Indian Natl. Sci. Acad., Part B, 54(4), 287-90; Process for preparing dichlorophosphorothioate esters, German Offen. 3716993; Preparation of alkyl phosphorodithioates, RO 91261; Process for preparing a S-substituted phosphorochloridothiolate, Eur. Pat. Appl. 219770; Efficacy of diaryl S-ethyl phosphorothiolates against root-knot nematode, Indian J. Agric. Sci., 56(8), 5976 05; O-Trihaloethyl phosphorodithioate pesticides, U.S. Pat. No. 4,457,923; S-tert-Alkyl phosphoroamidodithioate pesticides, U.S. Pat. No. 4,450,158; Oxidation of organophosphorus compounds, Ger. Offen. 3,033,957; Sulfuric acid derivatives as attractive oxidation agents for phosphorus (III) Compounds, Angew. Chem., 94(7), 560; Lower S-alkyldichlorothiophosphates, Czech Patent 189,342; Alkyl and aryl phosphorochloridothioates, Japanese Patent 55139394; Organophosphorus compounds, Ger. Offen. 2,635,931; Sulfenyl- and sulfinylphosphonic dichloride insecticides, U.S. Pat. No. 3,454,679; S-Substituted phosphorodichloridothioates, U.S. Pat. No. 3,337,658.
U.S. Pat. No. 4,056,581 describes the preparation of certain S-alkyl, -cycloalkyl, -aralkyl, and -aryl phosphorodichloridothiolates by reacting a sulfenyl chloride, which can be prepared in situ, with phosphorus trichloride and a carboxylic acid or water. This reference utilizes either water or a carboxylic acid as an oxygen donor. In the referenced process, one equivalent of sulfuryl chloride is consumed and one equivalent of carboxylic acid chloride or hydrogen chloride is generated as a byproduct (which must be removed, neutralized and disposed of). The present invention, unlike the process disclosed in U.S. Pat. No. 4,056,581, replaces half of the sulfuryl chloride with an inexpensive sulfur based acid which also serves as the full equivalent of the oxygen donor; therefore, no carboxylic acid chloride is generated, thereby obviating problems of its removal, neutralization and disposal.